Deep Marine Environment Research Articles

Uppermost Jurassic to Lower Cretaceous benthic foraminiferal faunas of the Weimei and the Bandingsi localities of northern and southern parts of South Tibet – A preliminary analysis

Diverse foraminiferal assemblages from the Weimei–Gyabula, and the Menkadun–Gucuo formations have been recorded based on the study of two Upper Jurassic to Lower Cretaceous successions, respectively located in the northern and southern parts of South Tibet. Each section contains three different foraminiferal assemblages. Due to the poor state of preservation and the occurrence of long-ranged cosmopolitan species, these foraminiferal assemblages do not allow a precise age assignment for the fossil bearing strata. However, the identification of the Globulina prisca assemblage indicates a Cretaceous age for the Shale Unit of the Gucuo Formation, although the Jurassic/Cretaceous (J/K) boundary was traditionally delineated above this unit. On the other hand, the occurrence of Dorothia oxycona indicates that the uppermost Gyabula and Gucuo formations cannot be older than Aptian and middle Albian age, respectively.During the Late Jurassic to Early Cretaceous, the northern part of South Tibet was located in a deep marine environment, probably at bathyal to abyssal depths, whereas the southern part of South Tibet was part of the outer neritic shelf environment. Typical foraminiferal associations of mildly oxygen-deficient deep-water environment and increased surface productivity have been recorded during the late Early Cretaceous. The biofacies succession indicates that the late Early Cretaceous was associated with a deepening of the palaeobasin, probably associated with a global Albian transgression.

Driving mechanisms of organic carbon burial in the Early Cretaceous South Atlantic Cape Basin (DSDP Site 361)

Abstract. Extensive black shale deposits formed in the Early Cretaceous South Atlantic, supporting the notion that this emerging ocean basin was a globally important site of organic carbon burial. The magnitude of organic carbon burial in marine basins is known to be controlled by various tectonic, oceanographic, hydrological, and climatic processes acting on different temporal and spatial scales, the nature and relative importance of which are poorly understood for the young South Atlantic. Here we present new bulk and molecular geochemical data from an Aptian–Albian sediment record recovered from the deep Cape Basin at Deep Sea Drilling Project (DSDP) Site 361, which we combine with general circulation model results to identify driving mechanisms of organic carbon burial. A multimillion-year decrease (i.e., Early Aptian–Albian) in organic carbon burial, reflected in a lithological succession of black shale, gray shale, and red beds, was caused by increasing bottom water oxygenation due to abating hydrographic restriction via South Atlantic–Southern Ocean gateways. These results emphasize basin evolution and ocean gateway development as a decisive primary control on enhanced organic carbon preservation in the Cape Basin at geological timescales (> 1 Myr). The Early Aptian black shale sequence comprises alternations of shales with high (> 6 %) and relatively low (∼ 3.5 %) organic carbon content of marine sources, the former being deposited during the global Oceanic Anoxic Event (OAE) 1a, as well as during repetitive intervals before and after OAE 1a. In all cases, these short-term intervals of enhanced organic carbon burial coincided with strong influxes of sediments derived from the proximal African continent, indicating closely coupled climate–land–ocean interactions. Supported by our model results, we show that fluctuations in weathering-derived nutrient input from the southern African continent, linked to changes in orbitally driven humidity and aridity, were the underlying drivers of repetitive episodes of enhanced organic carbon burial in the deep Cape Basin. These results suggest that deep marine environments of emerging ocean basins responded sensitively and directly to short-term fluctuations in riverine nutrient fluxes. We explain this relationship using the lack of wide and mature continental shelf seas that could have acted as a barrier or filter for nutrient transfer from the continent into the deep ocean.

Kurucaşile – Cide Dolayının Jeolojisi

Cide-Kurucaşile area on the İstanbul Zone is an important region for understanding the geological evolution of NW Anatolia and the Black Sea. The lowest visible unit of the region is the Carboniferous coal-bearing terrestrial sediments. Permian aged terrestrial Çakraz Formation and the overlying Triassic lacustrine Çakrazboz Formation unconformably overlie the Palaeozoic sequence. Dogger aged Himmetpaşa Formation represents a short-period marine invasion. The transgression that started in the Kimmerician on the Dogger and older units has led to the development of a carbonate platform, which has risen and demised after the Berriasian. A second carbonate platform, much more limited than the previous one, developed in the Late Barremian, and then the whole region deepened. The Cenomanian is a period of regional uplift and erosion. The first effective volcanic activity in the region started in the Middle Turonian. During this period, extensional faults coeval with the deposition of volcanic and volcanogenic clastics, and colluvial wedges developed in front of them, and the region gained an irregular topography. In the Middle-Late Santonian, the volcanism became silent for a while, the region rapidly subsided and became a completely deep marine environment. These events indicate that the continental crust of the region was totally broken up and the oceanic crust began to develop in the Western Black Sea back arc basin. In the Campanian, the volcanism reactivated much more intensely, but ceased after a short time, leaving its place to pelagic sediments forming the southern passive continental margin deposits of the Black Sea. In the Maastrichtian, the region was tectonically compressed and uplifted and provided turbiditic material to the Black Sea in the north and the Devrek Basin in the south. Siliciclastic turbidites have been deposited in the region until the Middle Eocene. At the end of the Middle Eocene, following uplifting of the entire region and the destruction of marine environments, the north-vergent thrusts were developed due to intense compression and the region became a fold-thrust belt. This compressional tectonic regime is probably still active.

Paleoenvironmental reconstruction of gold-bearing BIF from the Archean Cuiabá deposit based on petrographic and geochemical studies

In the world-class Cuiabá gold deposit, located in the Archean Rio das Velhas greenstone belt in Brazil, metamorphosed carbonate-dominated banded iron formations represent the main lithology hosting gold mineralization. The deposit's stratigraphy consists of a basal metavolcanic unit with carbonaceous metasedimentary rocks, followed by a layer of gold-bearing BIF and thin layer of carbonaceous metapelite, a upper metavolcanic unit, and turbiditic metapelites associated with metavolcanoclastic rocks. The BIF is essentially composed of fine-grained quartz and siderite, with variable contents of carbonaceous matter. It is assumed that these chemical sedimentary rocks, classified as Algoma-type BIF, have been formed in the deep-sea environment, relatively close to volcanic spreading centers. This hypothesis is supported by the BIF's geochemical signature, which in general presents a positive anomaly of La (La/La*paas = 0.64–3.43), Eu (Eu/Eu*paas = 1.27–4.05) and Y, reflecting characteristics inherited from seawater and high-temperature hydrothermal fluids (>250 °C). In addition, the commonly observed superchondritic Y/Ho ratio values reinforce the influence of seawater on the rock's geochemistry. The absence of Ce anomalies concerns the oxygenation conditions of seawater, indicating low oxygen availability. The low content of Al2O3 (<0,27%) and other immobile elements, typical of detrital sediments, corroborate the interpretation that these rocks have been deposited in a deep marine environment with low siliciclastic influence. Subordinately, ferruginous metachert, BIF with magnetite and BIF with silicates are also present in the Cuiabá gold deposit. This diversity may be related to specific changes in the basin during the deposition of ferruginous chemical sedimentary rocks - changes that may indicate, for example. variations in the detritic support or availability of carbonaceous matter. Furthermore, geochemical studies from the lower and upper mafic metavolcanic units of the Cuiabá gold deposit helped to constrain and provide a broader understanding of the depositional basin's geotectonic context. Consequently, a genetic model that includes the paleoenvironment of this sequence is proposed. Both rocks of the lower and upper units have very similar mineralogical composition, but register significant geochemical differences. The lower unit is a calc-alkaline basalt/andesite from a continental arc, interpreted as having been developed during the Rio das Velhas II event (2800-2760 Ma), while the upper unit is defined as basalt with a transitional affinity to tholeiitic, possibly corresponding to an ocean floor volcanism.

Benthic foraminiferal assemblages and biostratigraphy of the Antalo Limestone, Mekelle Basin, Northern Ethiopia

This study focused on the identification, detailed systematic descriptions and stratigraphical distributions of different foraminifera and other species to make the first systematic paleontological analysis, interpret paleoenvironment and determine the age of Antalo Limestone of the Mekelle Basin. Fieldwork and section logging, with sample collection at seven outcrop locations, followed by petrography and standard micropaleontological analysis were carried out. Abundant foraminifera fossils of 17 species were identified from 42 thin sections and 5 washed samples of marl and shale. The faunal assemblage also comprised dasyclad green algae, calpionellid, brachiopods and stromatoporoids (Cladocoropsis mirabilis). The benthic foraminiferal assemblage is represented by 3 species of the order Lituolida (Freixialina planispiralis, Nautiloculina circularis and N. oolithica), 11 species of the order Loftusiida (Alveosepta jaccardi, Choffatella tingitana, Conicokurnubia orbitoliniformis, Everticyclammina virguliana, Kurnubia jurassica, K. morrisi, K. palastiniensis, K. wellingsi, Praekurnubia crusei, Pseudocyclammina lituus and Siphovalvulina variabilis), 2 species of the order Textulariida (Redmondoides lugeoni and Valvulina lugeoni) and 1 species of the order Miliolida (Miliolinella quinquangula). The green algae comprised 3 species of the order Dasycladales (Clypeina jurassica, Salpingoporella annulata and Salpingoporella gr. pygmaea). The calpionellid is represented by 1 species of the order Calpionellidae (Calpionella alpina). The brachiopods comprised 2 species of the orders Rhynchonellida (Somalirhynchia africana) and Terebratulida (Somalithyris bihendulensis). Based on the stratigraphical distributions of these benthic foraminifera, dasyclad green algae, calpionellid and brachiopods, three zones namely; Kurnubia palastiniensis, Somalirhynchia africana/Somalithyris bihendulensis and Alveosepta jaccardi/Pseudocyclammina lituus have been established, signifying a Callovian – Oxfordian, a Callovian – Early Kimmeridgian and a Kimmeridgian – Tithonian ages respectively. Therefore, a Callovian – Tithonian age has been assigned to the Antalo Limestone. This faunal assemblage indicated a shallow – deep marine environment with normal marine salinity which has a strong affinity with the faunas of the Middle – Upper Jurassic Peri-Tethyan carbonates, indicating closely related geological evolution. Six benthic foraminiferal morphogroups have been identified, indicating epifaunal – infaunal microhabitats and active deposit-feeding, detritivorous, herbivorous, omnivorous, and bacterial scavenging feeding strategies.

Biostratigraphy and Sequence Stratigraphy and Depositional Environment of Kolosh Formation in Dohuk Area, Northern Iraq

The present study deals with biostratigraphy, depositional environment and sequence stratigraphy of Kolosh Formation in two sections of Bekher anticline, northeastern Iraq by using the planktonic and benthonic foraminifera. Therefore, (48) species of planktonic foraminifera belonging to (14) genera and (34) species of benthonic foraminifera belonging to (19) genera have been recognized. The detailed planktonic foraminiferal investigation permits the recognition of seven well defined biozones and three subzones; they indicate that Kolosh Formation extends from the Early Paleocene (Danian) to Late Paleocene (Thanetian) age. The depositional environment of the formation was studied throughout relying on the variation in the diversity of planktonic forminifera, as well as throughout the ratio of the planktonic foraminifera to the whole mass of foraminifera, and the ratio of planktonic forminifera to the benthonic formiminifera. The lower part of the formation represents the upper bathyal environment, while the middle part deposited within the outer shelf environment, then deposition basin became within the middle shelf area in the upper parts of the formation. Sequence stratigraphic analysis for the studied sections of Kolosh Formation delineated three sequences which is interpreted as 3rd order sequences, and it is found that the deposition of Kolosh Formation in the Badi section had been occurred in shallower level for most sedimentation intervals compared to the Linwa section which represents a somewhat deeper marine environment.

Late Jurassic-Early Cretaceous sandstones of Algan formation: composition, genesis, sources (North-West of Koryak Highland)

The article presents the results of studying the petrographic and mineralogical compositions of the sandstones of the Algan formation. Sandstones represented by pelitic-fine-medium-grained quartz-feldspar lithic arenites. Two tectonically combined sandstones lithotypes found. Lithotypes were formed in two heterochronous basins by high-speed and medium-speed turbidity flows, in moderately deep marine environments, in a relatively small distance from the coast. Sedimentation was near the deltas and prodeltas. The sources of these basins were different, related to the heterochronous volcanic areas in the north of the researched region.

Geochemistry of Eocene Bawang Member turbidites of the Belaga Formation, Borneo: Implications for provenance, palaeoweathering, and tectonic setting

The Belaga Formation of the Rajang Group or Rajang Fold and Thrust Belt (Late Cretaceous to Late Eocene) is mostly exposed in Sibu Zone along with some exposures in the Miri Zone of Central Sarawak. This entire turbiditic sequence was believed to have been deposited in a deep marine environment in a basin having an overall passive margin setting, that is, the Rajang Sea. However, the Eocene age‐related stratigraphic record of this group (including Bawang Member) is much more complex, due to the complicated geological and tectonic settings which prevailed during their deposition. Here, we present field observations along with the application of various geochemical proxies and their constraints for the understanding of provenance, palaeo‐weathering, and tectonic evolution of the area during the deposition of Bawang turbidites. Based on field observation, it has been found that this member consists of four main lithofacies, including massive sandstone facies (MSF), thick‐bedded facies (TBF), heterolithic facies (HF), and mud facies (MF). Using geochemical data, chemical weathering indices (CIA and CIW) values and A‐CN‐K plot show that the source area for Bawang turbidites has undergone a moderate to an intense degree of chemical weathering and was influenced by the recycling effect. The slight depletion in sandstones and shales for Cr, Ni, and V values is consistent with the felsic dominated source region; however, La/Sc versus Co/Th and La/Th versus Hf plots show a mixed source (felsic and intermediate volcanic source) with some input of recycled sediments from the older sedimentary to metasedimentary rocks. Various geochemical ratios and discriminant diagrams verify that the Schwaner Mountains and its metamorphic group of rocks were the principal provenances for these sediments, along with some input from West Borneo. The results of the geochemical analysis also show that Bawang turbidite sediments were deposited in a basin associated with an initial active continental margin setting and the basin was shifting towards a passive setting (Late Eocene–Oligocene). The volcanic input in Bawang Member during the Late Eocene also suggests the involvement of some subsequent possible arc setting around the “Bawang subbasin”.

The Cuticles of (?) Thylacocephalan Arthropod from the Basal Choteč Event (Choteč Formation, Eifelian; Barrandian Area, Czech Republic)

Abstract Small fragments of phosphatic cuticle have been observed in dark limestone of the early Eifelian age (Choteč Formation) in the interval of the Basal Choteč Event. The cuticle is two-layered, primarily folded, with a chamber between outer and inner walls. Fragments likely represent small cuticle pieces from the margins of the carapace. The exterior of the cuticle is nearly smooth bearing irregular network of wrinkled polygons or shallow pits. Low conical mound-like to high thorn-like spines with annular structure extend from both outer and inner surface of cuticle. Wrinkled and folded bases of these spines indicate moderate flexibility of cuticle. Spines are hollow, the higher ones often with apical opening. The inner surface of carapace carries smaller spines or is nearly smooth. Chamber walls inside the cara-pace are with folds and other structures supporting stiffness of the cuticle. The internal walls of the cuticle are covered by polygonal bumps. These uniformly sized and shaped bumps are about 1 μm sized and likely represents imprints of the epithelial cells adjoined to the basal membranous layer of endocuticle. Biological affinity of cuticle fragments is unclear. They surely represent pieces of the arthropod cara-pace, the most probably a thylacocephalan. Associated fossils indicate a deeper marine environment. Bloom of prasinophytes, abundance of dacryoconarids and organophosphatic brachiopods, and striking rarity and diminutive size of other fauna indicate eutrophic conditions in a neritic sea, likely with hypoxic bottom water. Nectonic mode of life in open sea can be suggested for an animal bearing this cuticle.

Fossil microbial shark tooth decay documents in situ metabolism of enameloid proteins as nutrition source in deep water environments

Alteration of organic remains during the transition from the bio- to lithosphere is affected strongly by biotic processes of microbes influencing the potential of dead matter to become fossilized or vanish ultimately. If fossilized, bones, cartilage, and tooth dentine often display traces of bioerosion caused by destructive microbes. The causal agents, however, usually remain ambiguous. Here we present a new type of tissue alteration in fossil deep-sea shark teeth with in situ preservation of the responsible organisms embedded in a delicate filmy substance identified as extrapolymeric matter. The invading microorganisms are arranged in nest- or chain-like patterns between fluorapatite bundles of the superficial enameloid. Chemical analysis of the bacteriomorph structures indicates replacement by a phyllosilicate, which enabled in situ preservation. Our results imply that bacteria invaded the hypermineralized tissue for harvesting intra-crystalline bound organic matter, which provided nutrient supply in a nutrient depleted deep-marine environment they inhabited. We document here for the first time in situ bacteria preservation in tooth enameloid, one of the hardest mineralized tissues developed by animals. This unambiguously verifies that microbes also colonize highly mineralized dental capping tissues with only minor organic content when nutrients are scarce as in deep-marine environments.

Foraminiferal biostratigraphy and paleoenvironmental analysis of the sediments penetrated by Sahaiawei-1 well in the Northern Delta Depobelt, Niger Delta Basin

Foraminifera biostratigraphy and paleoenvironmental analysis of the sediments penetrated by Sahaiawei-1 Well in the Northern Delta Depobelt, Niger Delta Basin was carried out in order to determine the foraminifera biozonation, age, paleobathymetry, depositional environment and paleo-oxygen condition of the well. The total foraminifera population recovered was two thousand, three hundred and sixty five (2365), with planktic foraminifera constituting one hundred and fifty four (154) forms, while calcareous benthic and agglutinated benthic foraminifera recovered accounted for two thousand, one hundred and sixty two (2162) and fourty nine (49) of the total foraminifera population respectively. The total foraminifera species recovered was fifty nine (59); planktic accounted for twenty (20) foraminifera species, while calcareous and agglutinated benthic foraminifera accounted for thirty one (31) and eight (8) foraminifera species respectively. Five benthic foramineferabiozones were identified: lumped P7-P13, P5-P6/P7, lumped P3-P4, lumped P1-P2 and M18 Zones of Blow (1969, 1979). The result of the analysis indicates that the entire analysed interval (1800ft – 10680ft) was deposited during the Late Maastrichtian to Late Eocene epoch. The depositional environments of the Well varied from littoral, marginal, shallow and deep marine environments.&#x0D; Keywords: Biozonation, Calcareous, Arenaceous, Agglutinated, Hyposaline Marshes, Hyposaline Shelf Sea

Reservoir characterization, Facies distribution, and sequence stratigraphy of Mishrif Formation in a selected oilfield, South of Iraq

Mishrif Formation is considered the most important between the reservoirs formations in the south of Iraq because of its geographic extent. The facies were predicted in Ratawi oilfield from wireline logs that divided Mishrif Formation into two main reservoirs separated by a barrier member. So the formation is almost cupped with shale intervals in both contacts of Rumaila Formations in the bottom and Khasib Formations in the top. While the reservoir characteristics were calculated using the log set in terms of petrophysical properties. The reservoir characteristics destroy and decrease to the south of Ratawi area because of the abundance the facies of the deep marine environments. Furthermore, it was predicted that Mishrif Formation has good reservoir characteristics to the other directions, especially to the east, contrary to the previous expectations.

Sedimentary history and palaeogeography of the Cenozoic clastic wedges of the Malaguide Complex, Internal Betic Cordillera, southern Spain

The Cenozoic sedimentary cover of the Malaguide Complex (Internal Betic Cordillera, Spain), in the Almería and Málaga areas, consists of a suite of sedimentary successions from continental and shallow-marine to deep-marine environments. Structural and stratigraphic relations, and petrological and geochemical signatures reveal the sedimentary evolution of the Cenozoic Malaguide Complex (CMC) from pre-orogenic (Palocene-Eocene) to syn-orogenic (Oligocene-Early Miocene) stages. Sandstones detrital modes of the overall succession are heterogeneous testifying to a multi-source area, marked by exhumation of the Malaguide basement terranes and of the Internal Betic Zone (Alpujárride Complex) in lower position. Pre-orogenic and syn-orogenic strata consist of four main depositional sequences: the Mula Group (Paleocene), the Xiquena Group (Eocene) for the preorogenic successions; and Ciudad Granada Group (Oligocene-Aquitanian) and Viñuela Group (Burdigalian) for the synorogenic successions. Pre-orogenic strata evolve from intra-arenite to hybrid arenites to progressive increase of sandstones in abundance of detrital supply from sedimentary cover of the internal Betic units. The unroofing history of the internal Betic Units, predominantly in the Malaguide Complex, is clearly testified in strata of the synorogenic clastic units, where detrital supply is coming from the Malaguide Complex. Sedimentary lithic fragments were derived from the Mesozoic strata of the Malaguide Complex while metamorphic detritus is related to the Internal Betic Zone basement that was exhumed starting from the Oligocene. Pre-orogenic mudrocks mainly show abundance of calcite and dolomite over quartz and phyllosilicates. Syn-orogenic mudrocks, record an abrupt decrease in calcite and dolomite and an increase of phyllosilicate, quartz and feldspars mainly in the Malaga section. The geochemical signatures attest to a compositional variation of the samples from pre-to-synorogenic successions, with palaeoweathering indices showing moderate values and a weak up-section decrease. The Cenozoic Malaguide Complex played a key role in the geodynamic evolution of the Betic Cordillera, representing the key tectonic element of the western Mesomediterranean domains.

Chasing the 400 kyr pacing of deep-marine sandy submarine fans: Middle Eocene Aínsa Basin, Spanish Pyrenees

In an attempt to understand the relative importance of climate and tectonics in modulating coarse-grained sediment flux to a tectonically active basin during what many researchers believe to be a greenhouse period, we have studied the Middle Eocene deep-marine Aínsa Basin, Spanish Pyrenees. We use orbital tuning of many spectral gamma-ray-logged fine-grained siliciclastic sections, already shown to contain Milankovitch frequencies, in conjunction with a new high-resolution palaeomagnetic study through the basin sediments, to identify polarity reversals in the basin as anchor points to allow the conversion of a depth-stratigraphy to a chronostratigraphy. We use these data, in conjunction with a new age model incorporating new biostratigraphic data, to pace the development of the deep-marine sandy submarine fans over c . 8 million years. Timing for the sandy submarine fans shows that, unlike for the fine-grained interfan sediments, coarse-grained delivery to the basin was more complex. Approximately 72% of the sandy fans are potentially coincident with the long-eccentricity (400 kyr) minima and, therefore, potentially recording changing climate. The stratigraphic position of some sandy fans is at variance with this, specifically those that likely coincide with a period of known increased tectonic activity within the Aínsa Basin, which we propose represents the time when the basin was converted into a thrust-top basin (Gavarnie thrust sheet), presumably associated with rapid uplift and redeposition of coarse clastics into deep-marine environments. We also identify sub-Milankovitch climate signals such as the c . 41.5 Ma Late Lutetian Thermal Maximum. This study demonstrates the complex nature of drivers on deep-marine sandy fans in a tectonically active basin over c . 8 Myr. Findings of this study suggest that, even during greenhouse periods, sandy submarine fans are more likely linked with times of eccentricity minima and climate change, broadly consistent with the concept of lowstand fans. However, hysteresis effects in orogenic processes of mountain uplift, erosion and delivery of coarse siliciclastics via fluvial systems to coastal (deltaic) and shallow-marine environments likely contributed to the complex signals that we recognize, including the 2–3 Myr time gap between the onset of deep-marine fine-grained sediments in the early development of the Aínsa Basin and the arrival of the first sandy fans. Supplementary Materials : Filtered records for each of the analysed gamma-ray logged sections. Anchor points, SARs tables and graphs and alternative tuning sections are available at: https://doi.org/10.6084/m9.figshare.c.5132975

Hyperpycnites within the Devonian-Carboniferous flysch of the Carpatho-Balkanides (Kostadinovica, eastern Serbia)

This study presents new discoveries of vascular plants and the trace fossil Dictyodora liebeana (GEINITZ) from the Devonian–Carboniferous Kučaj-Zvonce flysch of the Carpatho-Balkanides and the implications of this fossil association for its sedimentary setting. The occurrence of the described plant debris in a deep-marine environment indicates the presence of hyperpycnites within the siliciclastic turbidites exposed at the Kostadinovica locality. The sedimentological data and the characteristics of the fossil material support the proposed model in which the sediment was at least partially transported by hyperpycnite currents. Furthermore, based on the assessment to similar palaeofloras from comparable formations, the age of the fossil plants can be determined as Early Carboniferous. This can be used as an additional biostratigraphic criterion given the relative abundance of vascular plants in other localities of the Kučaj-Zvonce flysch described in previous studies. The age and the depositional setting of the succession is further better constrained by the first observation of Dictyodora liebeana (GEINITZ) in the Carpatho-Balkanides of Serbia.

Littorina and post-Littorina sedimentological processes in the Odra Channel in light of multidisciplinary investigations of a sediment core, Pomeranian Bay, southern Baltic Sea

A multi-proxy study was performed on a gravity core supplemented by acoustics profiles and new radiocarbon dates of macrofossils found in the sedimentation history of the Odra Channel during the Holocene. The channel is located in the western part of Pomeranian Bay and was shaped by a pre-Odra river that flowed northwest along the Peene valley and the eastern part of Rügen Island during a drop in Yoldia Sea level. The acoustic profiling enabled identification of glacial till, the Baltic Ice Lake and Littorina sediments. The studied core penetrated only marine sediments deposited during Littorina and Post-Littorina stages and was the subject of grain size, geochemical and diatom analyses. The age of appearance of a marine environment in the studied area was estimated at 7200 yrs BP. The performed studies enabled division of the core into three phases of environmental evolution: the Littorina I phase occurred during the time span 7200–6000 yrs BP and is described as a shallow water brackish basin with a low rate of sea level rise and favourable conditions for biogenic production, the Littorina II phase dated at 6000–3800 yrs BP reflects a deep marine environment with relatively high salinity and greater current velocity, and the last phase, Post-Littorina, covered the last 3800 yrs BP and turned out to be a strongly energetic environment with decreasing salinity. The change from Littorina II to Post Littorina phase correlates clearly with a change in the acoustic reflection. Core analyses could be associated with extreme stormy cold events known as Bond events dated at 5900–5500 yrs BP and 4200 yrs BP evidencing the final destruction of the Odra Bank barrier.

Lithofacies, particle size analysis and paleodepositional environment of the Eze-Aku Group (Cenomanian–Turonian) in the Itigidi-Ediba area, Afikpo Synclinorium, southeastern Nigeria

Field, lithofacies and particle size analysis of sediments of the Eze-Aku Group in the Itigidi-Ediba localities, Afikpo Synclinorium, were carried out to describe the textural attributes of the sediments and reconstruct the paleodepositional environment of the study area. Field studies show that the geology is characterized by a succession of marine shales and shaly-limestone overlain by elongate sandstone ridges that trend in a northeast–southwest direction. In certain cases, the sandstone ridges alternate with shales. These deposits are characterized by wave and tide generated sedimentary structures with trace fossil assemblages consisting mainly of Ophiomorpha, Skolithos, and Cruziana ichnofacies that are suggestive of a moderately disturbed environment. Lithofacies studies of the sedimentary succession indicates five facies associations: conglomeritic consolidated sandstone, laminated sandstone, bioturbated sandstone, laminated shaly-limestone and cross-bedded sandstone facies associations suggesting deposition in proximal sub-marine, shelf edge/sub-marine fan, distal sub-marine fan/distal shelf, shallow/deep marine, and shoreface/foreshore sub-environments, respectively indicating a tidal shallow shelf to deep marine environment. Analysis of the grain size spectrum in some selected outcrops shows sediments that are moderate to poorly sorted, generally positively and very positively skewed and mesokurtic, platykurtic to leptokurtic, deposited in a shallow marine environment under moderate to high energy conditions, with fluvial influence.

Foraminifera Biostratigraphy, Palynofacies and Paleoenvironment of deposition of the Albian to Santonian sediments in the Southern Benue Trough, Nigeria

The Albian-Santonian sedimentary sequence in the Ndeaboh-Nenwe area of Enugu, Southern Benue Trough, were analysed for foraminifera and integrated with ostracod and palynofacies analyses to comprehensively appraise the age and depositional environment of the sediments. This is paramount since the studied formations have intermittent series of non-marine sedimentary influences throughout the basin. The results of foraminifera evaluation indicate that the Abakaliki Formation is barren of foraminifera species, whereas the Eze-Aku and Awgu formations have preponderance of planktonic foraminifera assemblages over benthic forms. The Eze-Aku Formation records an abundance of species of Hedbergella and a peak for Heterohelix. The co-occurrence of Whiteinella archeocretacea, Hedbergella planispira, Heterohelix delrieonsis and the ostracod species Ovocytherida symmetrica, suggests a Late Cenomanian to Early Turonian age. Rare species of short-ranging and keeled planktonic taxa are present in Awgu Formation, which has a preponderance of Heterohelix reussi, Heteroheix globulosa, Heterhelix pulchra, Whiteinella baltica, and the ostracods Brachycythere ekpo and Cythereis sp. The Awgu Formation is Middle Turonian to Santonian. The percentage of amorphous organic matter and lithologic characteristics suggest a marine environment for the Abakaliki Formation, although the water depth cannot be ascertained. In the Eze-Aku Formation, the prevalence of Hedbergella and its co-occurrence with Whiteinella and associated palynofacies data (amorphous organic matter, black debris, few structured terrestrial phytoclasts) and dinoflagellate cysts suggest a fairly deep (200–300 m) marine environment with occasional terrestrial input. The low diversity of agglutinated benthic foraminifera assemblage in the Awgu Formation indicates deposition at a minimum paleo-water depth. The paucity of benthic foraminifera, rare occurrence of keeled planktonic species, and the dominance of Hedbergella and Heterohelix; low oxygen tolerant species, in the studied interval are attributed to anaerobic bottom conditions possibly caused by poor bottom water circulation and high organic productivity in the oceans and seas during the Cenomanian-Santonian.

Full-Path Compensated Least-Squares Reverse Time Migration of Joint Primaries and Different-Order Multiples for Deep-Marine Environment

In the deep-marine environment, seismic data contain multiples and are seriously affected by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> attenuation. Multiples have been used in migration to image the shadow zones and improve the resolution. However, the effect of attenuation on multiples is more serious than primaries because multiples have longer propagation paths. Therefore, we compensate the forward-propagated source-side and backward-propagated receiver-side wavefields along all the propagation paths of multiples. To fully use the primaries and multiples, we construct an objective function of least-squares reverse time migration of joint primaries and multiples (LSRTM-J) to update the imaging results by jointly using primaries and different-order multiples. In practice in a seawater medium, seismic waves can hardly be affected by attenuation. To decrease the computational cost, we divide the medium in the deep-marine environment into an acoustic medium part and a viscoacoustic medium part and derive the acoustic–viscoacoustic coupled compensated forward continuation operator, compensated adjoint operator, attenuated demigration operator, and gradient formula of joint primaries and multiples. To eliminate the severe scattering and diffracted noise caused by the strong-reflected irregular seabed interface, we mesh the velocity and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> models into curvilinear grids to perfectly match the seabed structure and realize the proposed viscoacoustic LSRTM-J in the curvilinear domain. Numerical examples on two typical models and a real data test suggest that the proposed method produces images with high SNR, high resolution, balanced amplitude, clear imaging structures, and strong deep region energy, and the total computational cost is the least of the other four conventional methods.

Age, depositional environment, and tectonic significance of an Early Neoproterozoic volcano‐sedimentary sequence in the eastern Beishan orogenic belt, southern Central Asian Orogenic Belt

The Beishan orogenic belt, located in the southern Central Asian Orogenic Belt, includes several discrete arc terranes. Here, we report on a newly discovered Early Neoproterozoic volcano‐sedimentary sequence in the eastern Beishan orogenic belt in order to constrain the composition and origin of the Shuangyingshan‐Huaniushan Terrane. The ~766‐m‐thick volcano‐sedimentary sequence is very low‐grade metamorphosed, and characterized by muddy and silty slate with the well‐developed parallel laminations and minor thinly‐bedded limestone in its lower and upper sections, and thick packages of sandstone‐conglomerate and basaltic rocks in the middle section. Lava flow units in the basalt are very common, and the sandstone‐conglomerate exhibits sedimentary structures typical of gravity currents, including erosional and slump features, and Bouma sequences. These features suggest that syn‐sedimentary volcanism occurred and the sequence formed in an active, deep marine environment. The basalt has a zircon U–Pb age of 901 ± 10 Ma, indicating that this sequence formed during the Early Neoproterozoic. Basalt samples have moderate SiO2 (45.33–49.18%), and high TiO2 (1.27–4.04%) contents, Mg# values of 25–48, and plot in the alkali basalt field in the Nb/Y versus Zr/TiO2 diagram, indicative of an evolved alkali basalt magma. They show inclined chondrite‐normalized REE patterns with (La/Yb)N ratios of 4.74–6.53, no pronounced negative Eu anomalies (Eu/Eu* = 0.87–1.22), no obvious negative Zr, Hf, Nb, and Ta anomalies in the primitive‐mantle‐normalized trace‐element diagram, consistent with oceanic island basalts. Considered together, these lithologies resemble those of an oceanic seamount. Our results, and the presence of the previously reported Gubaoquan granitic and mafic rocks (905–865 Ma) that formed in an active continental margin setting and underwent an amphibolite‐facies metamorphism, suggest that the Shuangyingshan‐Huaniushan Terrane may be an accreted terrane that consists of different lithologies with various origins that formed during the Neoproterozoic.